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Originally Posted by afarre
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If we were to use the USB host all the time with a powered HUB,
do you think we need USBHPEN and USBHPWR?
I know for sure a USB hub does not require to get power from host when used self-powered. I know if because I have a PC with one USB host power burned and it still works when I place a powered hub.
My doubt is if it will be required to force USBHPWR to some state all the time just to let CPU know there is no fault condition.
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Close - check the USB host schematics from the Intel eval sheets (pg29) and you will see that there are two control lines going to the MAX1693 USB power control chip. One is the over current sense output to the CPU (USBHPWR) and the other turns on (or off in the case of an overcurrent condition) the 5V to the external device (USBHPEN).
We probably don't need those signals. However, we DO need a signal conditioning/transient-protection device similar to the STF201 USB interface chip between our external device and the CPU.
One interesting observation from those schematics on page 29 - note the 15K pulldown resistors...:approve: